Drift and ground speed meter



July 28,1936. a P. v. H. wEEMs ET AL 9,

DRIFT AND GROUND SPEED METER Filed May 15, 1934 4 Sheets-Sheet 1 INVENTORS PhlL/F v. H. WEEMS BY ROBERT HENR/CH July 28, 1936.

Filed May 15, 1934 4 Sheets-Sheet 2 INVENTORi PHIL/P V.H. WEEMS BY ROBERT HENR/Ch' ATTONEY July 28, 19 6. RV. HWEEMS HAL 2 9,

DRIFT AND GROUND SPEED METER Filed May 15, 1934 4 Sheets-Sheet 3 INVENTORS PHIL/P V h. WEEMS BY ROBERT HEIYR/CH July 28, 1936. PIV: H. WEEMS ET AL DRIFT AND GROUND SPEED METER 4 Sheets-Sheet 4 Filed May 15, 1934 lNVENTdRS PHIL/P 1 H. WEEMS BY ROBERT HEIVR/CH Patented July 28, 1936 UNITED STATES DRIFT AND GROUND SPEED Philip V. H. Weema and Robert Heinrich, San Diego, Calif,

This invention relates to a meter for indicating the drift and ground speed of an aircraft and has among its various objects to provide an instrument for the purpose mentioned having a member movable at different speeds to synchronize it with the relative movement of an object on the ground, means to introduce the altitude argument into the indication of the instrument, and means actuatable by the air stream flowing past the craft to drive the aforesaid member.

A further object is to provide an instrument of the type mentioned that does not require the eye of the observer to be positioned at any particular point.

In the drawings:

Fig. 1 is a side elevation of the present tion;

' Fig. 2 is a top plan view thereof;

Fig. 3 is a perspective top view with the lens support moved relatively out of position so it will be shown in the drawings;

Fig. 4 is a sectional view of the indicating and sighting mechanism substantially on the line 4-4 of Fig. 2.

We are aware that heretofore ground speed meters have been devised that utilize the principle of a moving member synchronizable with the relative movement of an object on the ground but in all of these with which we are acquainted it is necessary that the eye of the observer be positioned at some particular point to obtain correct readings. With the present invention no such restriction upon the position of the eye is required since an image of the ground beneath the aircraft is projected to be visible in conjunction with, and substantially in the same plane as, the sighting point on the synchronized member.

The supporting ring 5 is fixed to the aircraft structure by means of bolts or screws passed through the ears 6. As is shown in Fig. 4, the uppermost inner edge of the ring 5 is bevelled and upon the face I thus formed a face on flange 8 rides to support a ring 9 that carries the mechanism to provide for rotation thereof for measuring the drift angle, as will be hereinafter set forth. Mounted upon the ring 9 is a housing l0 within which is disposed an air-driven motor having radial blades I2 fixed to a hub l3 that has driving engagement with a shaft M. An air intake member l5 that may be supported to rotate with ring 9 has formed in it a passage i6 having an enlarged mouth that merges into contracted passage that is connected by a tube I! to the housing It); the mouth of passage It being directed forwardly of the craft, a stream of air is forced throimh tube inven- I1 and discharged against blades I2 which causes the blades to rotate and drive shaft i i, the exhaust air exiting through opening 53. The speed of rotation of shaft i4 is controlled by means of a screw i8 disposed to be movable to close the outlet of tube i1 whereby the quantity of air admitted to impinge upon blades I; may be adjusted to drive the shaft It at such speed that the apparent or virtual movement of helical thread l9 along shaft I4 will synchronize with the movement of an object on the ground.

To avoid the necessity of observing the thread I9 .from any fixed point or points a translucent screen 20, which may be of frosted glass, celluloid, or the like, is placed immediately above the thread I! and by means of a suitable lens 2! supported by a barrel 5% an image of the ground heneath the craft is projected upon screen 20, thus bringing the image of the ground into substantially the same plane as is the observed point on thread l9 and hence the image and the thread may be viewed simultaneously with the eye of the observer in any convenient position. It is apparent that any given object in the image of the ground will appear to move across the screen 20 and also that the space between any two adjacent turns of thread l9. will likewise have an apparent movement across the screen. it being understood that shaft M is disposed parallel to the path of the craft and that the direction of rotation of the shaft is such as to cause the above mentioned apparent movement of a space between adjacent turns on thread l9 to follow the relative movement of an object upon the ground.

One end of shaft it is iournalled in a casing 2i mounted upon ring 9 opposite the housing it. the end of. shaft it inside the casing 2i having in it a slot 22 for feathering upon the shaft a friction disk 23 that is connected by a yoke 24 to traveling nut 25 upon screw 26 whereby the friction disk 23 is moved longitudinally of shaft I 6 when the screw 26 is rotated. Upon one end of screw 26 is fixed a gear 2! that is meshed with a gear 28 carried on one end of the shaft that has upon its upper end a bevelled pinion 29 that meshes with a pinion 30 mounted to rotate with a worm gear 3i. Engaged with gear 3| is a'worm 82, on a shaft 33 that carries at its upper end a pinion 36 meshed with internal gear 35 on ring 3% that is rotatably mounted on the upper end of casing 38.

on a supporting member 39 that is fixed to a plate 40 secured to casing 2|, there being an index 69 carried by ring 36 to scale.

An altitude scale 31 is inscribed upon a plate 38 mounted project over the altitude A disk 42 is rotatably mounted and disposed with one face in driving contact with the frictionthe metal of disk 45 and flange 45 that will tend to drag disk 45 around with the magnet but the rotation of disk 45 is opposed by a helical spring 41 having one end connected to member 33 and the other end thereof connected to spindle 45 upon which disk 45 is mounted. Since the currents induced in disk 45 by magnet 44 will be proportional to the speed of rotation of the magnet, the force exerted to drive the disk 45 around with the magnet will also be proportional thereto and consequently the angular movement of disk 45 against the effort of spring 41 will be a function of the rotational speed of magnet 44 and consequently the greater the rate of such speed of rotation, the greater the displacement of disk 45 from its position of rest. Upon the uppervsurface of disk 45 is a scale of ground speeds that is visible through apertures 49 and 50 in the members 33 and 38, respectively. The mechanism is protected from the weather and dirt by a glass cover 56.

The mode of operation is as follows: The device is rotated in ring 5 until the axis of shaft I4 is parallel with the relative movement of objects upon the ground and the drift, if any, is read from the scale 5| or 52 on ring 5 opposite lubber lines 55 on member 9, depending upon whether the drift is right or left. Screw I8 is adjusted so that shaft I4 and thread is will be given such rotational speed that when an object in the image on the ground as seen on screen 20 is once brought into coincidence with the space between two adjacent turns of thread l9, such object will move across the screen at the same rate as the apparent movement of the space between the threads. This makes the indication of the instrument proportional to the ground speed. Ring 35 is rotated to bring the altitude at which the craft is flying opposite index 4| which rotation, through gear 3|, shaft 33, worm 32 and the mechanism connecting the worm 32 to disk 23, changes the position of disk 23 with respect to the center of disk 42 and therefore the speed at which the disk 42 is driven is made a function of the altitude. It is obvious that when the friction disk 23 is moved nearer the center of disk 42, the latter will be driven more rapidly for a given speed of rotation of shaft l4, and vice versa; hence any change in the setting of ring 36 corresponding to a difference in altitude will introduce into the rate at which magnet 44 is driven a corresponding change and thus the speed read from disk 45 is a function of both the ground speed and the altitude of the craft.

The invention described herein may be manufactured and used by or for the Government of the United States for governmental purposes, without the payment of any royalties thereon.

We claim:

1. A device of the class described comprising, in combination, driving means adjustable as to speed and actuatable by the stream of air past an aircraft in flight, means afl'ording a uniformly linearly moving sighting point driven by the said means, a rotatably mounted disk, a magnet carried by said disk, a rotatable speed-indicating dial mounted to be inductively driven by said magnet, means to apply to said dial a reverse torque proportional to the angular displacement of said dial, means forming a driving connection between said second mentioned means and said disk, means to position said driving connection at a distance from the center of said disk that is inversely proportional to the altitude of the craft, a translucent member through which said sighting point is visible, and means to project upon said member an image of the ground beneath the craft.

2. A device of the class described comprising, in combination, driving means adjustable as to speed and actuatable by the stream of air past an aircraft inflight, a rotatable shaft driven by said driving means, a helical thread on at least a portion of said shaft, a rotatably mounted disk, a magnet rotatable with said disk, a rotatable speed-indicating dial mounted to be inductively driven by said magnet, resilient means to restrain the rotation of said dial by said magnet, a friction disk feathered on said shaft and having its periphery bearing on the aforesaid disk, a rotatable altitude scale settable at the altitude of the craft, means connecting said altitude scale and said friction disk to set said friction disk radially of said first disk at distances from the center of said first mentioned disk that are inversely proportional to the altitude setting, a light-permeable member through which said helical thread is visible, and means to project upon said member an image of the ground beneath said craft.

3. A device of the type described comprising, in combination, an air-driven rotor, means to direct upon said rotor a current of air taken from the air stream passing the craft upon which the device is mounted, means to vary the said current and thereby control the speed of said rotor, a shaft driven by said rotor, means on said shaft providing a linearly moving sighting point as the shaft rotates, magnetic speed-indicating mechanism, means forming a driving connection between said shaft and said mechanism including variable speed means, means to vary the effect of said driving means upon said mechanism to introduce into the indication of said mechanism the factor of the altitude of said craft, and means to project an image of the ground beneath said craft to be viewable in conjunction with said sighting point.

4. A device of the class described, comprising a rotatable member providing a linearly moving sighting point, a linearly shiftable disk rotatably driven by said member, a speed indicator of the magnetic inductive type including a disk having frictional driving contact with the said shiftable disk, a travelling nut connected to said shiftable disk to shift the same, a rotatable screw engaged with said nut and fixed against longitudinal movement, a skew gear fixed on said screw, 9. like gear engaged therewith, a shaft on which said like gear is mounted, a bevel pinion on the last mentioned shaft, a bevel gear meshed with said pinion, a worm gear connected to said bevel gear, a worm meshed with said worm gear, a gear fixed to the shaft of said worm, and a rotatable altitude indicating device having gear teeth meshed with the gear fixed to the worm shaft, whereby setting of said altitude indicating device. sets said shiftable disk to a radial position on the disk cooperating therewith to drive said cooperating disk at a rate that is a function of the altitude.

5. A device of the class described, comprising a rotatable member providing a linearly moving sighting point, a speed indicator, variable speed driving means to drive said indicator from said member, and means to vary the speed of said driv ing means including a traveling nut operatively connected to said driving means, a rotatable screw fixed against longitudinal movement and engaged with said nut to shift the same, a skew gear fixed to said screw, a shaft adjacent thereto, a second skew gear on said shaft meshed with the first mentioned gear, a bevel pinion on said shaft, a bevel gear meshed with said pinion, a worm gear connected to said bevel gear, a worm meshed with said worm gear, a gear fixed on the shaft of said worm, and a rotatable altitude indicating device having teeth meshed with the gear on said worm shaft whereby the speed of said driving PHILIP V. H. WEEMS. ROBERT HENRICH. 

